fix(openai): strip pattern keyword from Responses API schemas (zod v4 compat)

.changeset/fix-openai-responses-pattern-keyword.md

@@ -0,0 +1,5 @@
+---
+"@ai-sdk/openai": patch
+---
+
+Fix `server_error` in OpenAI Responses API when schemas generated by zod v4 contain `pattern` keywords with unsupported regex features (e.g. lookaheads from `z.email()`, `z.uuid()`). The `pattern` keyword is now stripped from response format schemas and tool parameters before they are sent to the API.

packages/openai/src/responses/openai-responses-language-model.ts

@@ -1,3 +1,4 @@
+import { removePatternKeyword } from './openai-responses-sanitize-schema';
 import {
   APICallError,
   type JSONValue,
@@ -345,7 +346,7 @@ export class OpenAIResponsesLanguageModel implements LanguageModelV4 {
                     strict: strictJsonSchema,
                     name: responseFormat.name ?? 'response',
                     description: responseFormat.description,
-                    schema: responseFormat.schema,
+                    schema: removePatternKeyword(responseFormat.schema),
                   }
                 : { type: 'json_object' },
           }),

packages/openai/src/responses/openai-responses-prepare-tools.ts

@@ -23,6 +23,7 @@ import type {
   OpenAIResponsesFunctionTool,
   OpenAIResponsesTool,
 } from './openai-responses-api';
+import { removePatternKeyword } from './openai-responses-sanitize-schema';
 
 type OpenAIToolOptions = {
   deferLoading?: boolean;
@@ -404,7 +405,7 @@ function prepareFunctionTool({
     type: 'function',
     name: tool.name,
     description: tool.description,
-    parameters: tool.inputSchema,
+    parameters: removePatternKeyword(tool.inputSchema),
     ...(tool.strict != null ? { strict: tool.strict } : {}),
     ...(deferLoading != null ? { defer_loading: deferLoading } : {}),
   };

packages/openai/src/responses/openai-responses-sanitize-schema.ts

@@ -0,0 +1,52 @@
+// OpenAI structured outputs rejects JSON Schema `pattern` values that contain
+// regex features it does not support (e.g. lookaheads). zod v4's toJSONSchema()
+// emits `pattern` for string validators like z.email(), z.uuid(), z.iso.date().
+// Strip the keyword recursively before sending schemas to the Responses API.
+//
+// Only standard JSON Schema structural keys are recursed into, so that tool or
+// response parameters whose name happens to be "pattern" are never touched.
+export function removePatternKeyword<T>(schema: T): T {
+  if (!schema || typeof schema !== 'object') return schema;
+  if (Array.isArray(schema)) return schema.map(removePatternKeyword) as unknown as T;
+
+  const result = { ...(schema as Record<string, unknown>) };
+
+  // Remove the JSON Schema string-validator keyword at this level.
+  delete result['pattern'];
+
+  // Keys whose values are { name → schema } maps. Recurse into the schema
+  // values but preserve the keys — a key named "pattern" here is a user-
+  // defined property name, not the JSON Schema keyword.
+  for (const mapKey of ['properties', 'patternProperties', '$defs', 'definitions']) {
+    if (
+      result[mapKey] &&
+      typeof result[mapKey] === 'object' &&
+      !Array.isArray(result[mapKey])
+    ) {
+      result[mapKey] = Object.fromEntries(
+        Object.entries(result[mapKey] as Record<string, unknown>).map(
+          ([k, v]) => [k, removePatternKeyword(v)],
+        ),
+      );
+    }
+  }
+
+  // Keys whose values are sub-schemas or arrays of sub-schemas.
+  for (const schemaKey of [
+    'items',
+    'allOf',
+    'anyOf',
+    'oneOf',
+    'not',
+    'additionalProperties',
+    'if',
+    'then',
+    'else',
+  ]) {
+    if (result[schemaKey] !== undefined) {
+      result[schemaKey] = removePatternKeyword(result[schemaKey]);
+    }
+  }
+
+  return result as unknown as T;
+}